EMPIRICAL-METHOD TO CORRELATE AND TO PREDICT THE VAPOR-LIQUID-EQUILIBRIUM AND LIQUID-LIQUID EQUILIBRIUM OF BINARY AMORPHOUS POLYMER-SOLUTIONS

A previous method of the author is modified in order to ensure (i) a b etter evaluation of the solvent activity coefficients at infinite dilu tion and (ii) the calculation of liquid-liquid equilibrium (LLE) for a thermal solutions also. The first goal is obtained by imposing that th e epsilon parameter, which corrects the entropic term of the Flory-Hug gins equation as required by the previous work, varies not only accord ing to the density of pure components but also according to the molar volume compositions. The second problem, linked to the demixing phenom ena occurring at the upper and lower critical solution temperature (UC ST and LCST) points for athermal solutions also, suggested a simple mo dification of the enthalpic term. It is assumed that the chi parameter is not nil for nonpolar mixtures also when the density of pure polyme r is remarkably different from the mixture density. While the method i s predictive for vapor-liquid equilibrium (VLE) and the weight fractio n activity coefficients at infinite dilution, the LLE data can only be correlated by using ''ad hoc'' empirical parameters. Further, an empi rical procedure is proposed to predict the UCST and LCST points of bot h polar and nonpolar mixtures which requires only the knowledge of the molecular weight of solvents and the density of polymers. A compariso n is made with well-known literature methods which predict the equilib rium data for many systems in both the VLE and LLE ranges.